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    <title>Document</title>
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    <script>
        // 根据位置返回字符 

        let str ='abcdef';
        // 1. charAt (index) 根据索引号返回字符 
        
        console.log(str.charAt(1)); //b

        // 2. charCodeAt(index) 返回相应索引号的字符 ASCII  
        console.log(str.charCodeAt(0));

        // 3. str[index] H5 新增
        console.log(str[0]);  a
    </script>
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